• Journal of the Korean Society for Precision Engineering
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• v.17 no.6
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• pp.111-118
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• 2000

The design of reference trajectory with respect to drag acceleration is necessary to decelerate from hypersonic speed safely after atmosphere re-entry of space vehicle. The re-entry guidance design involves trajectory optimization, generation of a reference drag acceleration profile with the satisfaction of 6 trajectory constraints during the re-entry flight. This reference drag acceleration profile can be considered as the reference trajectory. The cost function is composed of the accumulated total heating on vehicle due to the reduction of weight. And a regularization is needed to prevent optimal drag profile from varying too fast and achieve realized trajectory. This paper shows the relations between velocity, drag acceleration and altitude in drag acceleration profile, and how to determine the reference trajectory.

• Wind and Structures
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• v.9 no.3
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• pp.245-254
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• 2006

The pressure and drag measurements were carried out in the wind tunnel to investigate the drag reduction of the disk by using an interference rod placed upstream. The results indicate that there is a pair of standing vortices in the front stagnation region of the disk induced by the rod. The standing vortices can decrease the pressure on the disk upwind side; hence it can reduce the drag of the disk. With an increasing rod diameter, the standing vortices are strengthened and more drag reduction can be achieved for the disk. With rod diameter d/D = 0.05 (d, D are the diameters of rod and disk, respectively), the total drag of the disk can be reduced by about 9% compared with that of the bare disk.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.483-486
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• 2002

Injection of microbubbles and/or polymer solution has been known to be a promising method for the reduction of frictional drag of water-borne vehicles. Naval Architects have been interested in friction drag reduction technology, since the friction drag of a commercial ship can be over $70{\%}$ of total resistance. The reduction of friction drag is also important for autonomous underwater vehicles and naval submarines to improve their durability and survivability In this study two sets of experiments were carried out for the friction drag reduction of 2-D channel wall and flat plate in the circulating water channels in Chungnam National University. Preliminary results from the experiments are presented and discussed.

• 한국전산유체공학회:학술대회논문집
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• 1998.05a
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• pp.67-74
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• 1998

Reducing drag of vehicles are the main concern for the body shape designers in order to lower fuel consumption rate and to aid the driving stability. The drag of bluff bodies like transportation vehicles is mostly pressure drag due to the flow separation, which can minimized by controlling the location and size of the separation bubble. In the present study, the TURBO-3D code is incorporated with optimal algorithm based on analytical approximation method to obtain optimal afterbody shape of the MIRA Model corresponding to the lowest drag coefficient. For this purpose three mutually independent afterbody angles are chosen as design variables, while the drag coefficient is chosen as an objective function. It is demonstrated in the present study that an optimal body shape having lowest drag coefficient which is about $6\%$ lower than that of the original shape has been successfully obtained within number of iterations of the optimal design loop.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.555-560
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• 2000

An experimental study on pumping characteristics of various turbo-type drag pumps is purformed. The inlet pressures are measured for various outlet pressures of the test pump. The maximum compression ratios for nitrogen are 100,000(Disk-type drag pump+ turbo molecular pump), 10000(Helical-type drag pump+turbo molecular pump), 850 (Helical-type drag pump), 100(disk-type drag pump).

• Fire Science and Engineering
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• v.5 no.2
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• pp.21-35
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• 1991

As a part of studies of drag reduction phenomenon, at the entrance flow region of abrupt contraction tube flowing water, dilute and concentrated drag reducing polymer solutions contraction losses are estimated experimentally. Futher more, entrance lengths are considered theoretically and are measured experimentally. In the present experiment, fluid temperature is fixed l$0^{\circ}C$ and flow rates are 3,000

• Fire Science and Engineering
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• v.5 no.2
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• pp.11-20
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• 1991

Dilute polymer solutions were injected into turbulent pipe flow of a Newtonian fluid. The local drag reduction for injection of polymer solution at the pipe wall was larger than that at centerline. From the above result we may conclude that the polymer additives were found to influence the flow in the neighborhood of the wall. The effects of the injection apparatus on the local drag reduction are small compared to the drag-reducing effects. The extent of drag reduction increased with polymer concentration and injection flow rate, and the maximum drag reduction obtained were 47% for Polyox Coagulant and 35% for Separan AP-273. In respect to polymer degradation, the polyacrylamide showed better shear stability than the polyethyleneoxide and thus the former expected to have a sharper molecular weight distribution.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.4
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• pp.59-67
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• 2004

Direct numerical simulations of turbulent flows over riblet-mounted surfaces are performed to educe the mechanism of drag reduction by riblets. Numerical simulations are performed for flow fields with R $e_$\tau$/=180. For riblet ridge angle $\alpha$=60$^{\circ}$, two different riblet spacings of $s^+/=20 and 40 are used in this study. The computed drag on the riblet surfaces is in good agreement with existing computational and experimental data. The mean velocity profiles show upward and downward shifts in the log-law for drag-decreasing and drag-increasing cases, respectively Turbulence statistics above the riblets are computed and compared with those above a flat plate. The purpose of this study is in two categories: first, to understand the drag reduction mechanism on riblet surface, second, to verify our own code by comparison of the present results with those from previous studies.udies.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.5
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• pp.223-227
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• 2002

Wind tunnel test or CFD is used for predicting aerodynamic drag coefficient in domestic motor companies. But, wind tunnel test requires much cost and time, and CFD has a relatively large error. In this study a predicting program of the aerodynamic drag coefficient based on empirical techniques was developed. Also GRG method was added to the program in order to decide optimal values of some parameters. The program was applied to 24 cars and the aerodynamic drag coefficients were predicted with 4.82% average error. Optimization was also accomplished to 6 cars. Some parameters to be modified were determined (1) to reduce the afterbody drag coefficient to the value established by a designer and (2) to preserve the same drag coefficient as the original automotive when some parameters have to be changed in the viewpoint of design. It was verified that the developed program can predict the aerodynamic drag coefficient appropriately and determine optimal values of some parameters.

• Journal of the Korea Institute of Military Science and Technology
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• v.2 no.2
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• pp.70-82
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• 1999

During the aircraft conceptual design stage, rapid aerodynamic analyses over various configurations are required. Hence, empirical and analytical methods play important roles in predicting the aero-dynamic characteristics. In this study, total drag estimation method based on empirical and analytical approaches is developed. By comparing with the results of the wind tunnel experiment and existing prediction methods, it is demonstrated that the developed method is accurate and useful in predicting total drag for the whole Mach number range.